Conventionally, as an exposure apparatus used for manufacturing a semiconductor device, there have been known an apparatus called a stepper and an apparatus called a scanner. The stepper reduces a pattern image formed on a reticle and projects the pattern image onto a wafer via a projection lens while moving step by step the semiconductor wafer on a wafer stage below the projection lens, thus sequentially exposing a plurality of portions on one wafer.
The scanner relatively moves a semiconductor wafer on the wafer stage and the reticle on a reticle stage with respect to the projection lens, irradiates the wafer with slit-shaped exposure light during scanning movement, and projects the reticle pattern onto the wafer.
The stepper and scanner are considered to be the mainstream of exposure apparatuses in terms of the resolution and overlay accuracy.
Such an exposure apparatus has a wafer stage which moves a wafer at high speed and aligns it. When the stage is driven, the acceleration/deceleration of the stage generates the reaction force of an inertial force. Transmission of this reaction force to a stage base causes swings and vibrations of the stage base. Additionally, such swings and vibrations induce natural vibrations in the mechanism of the exposure apparatus, and high-frequency vibrations occur. This may interfere with high-speed, high-precision alignment.
In order to avoid this direct transmission of the reaction force to the stage base, the following structures are considered to be the mainstream: the stator of a linear motor which drives the stage is supported on a floor independently of the stage base, the stator can be so moved as to cancel the reaction force generated during stage movement, or the vibrations of the device with the movable stator are reduced by applying a compensation force, which is equivalent to the reaction force of the stage base.
These days, the acceleration in driving the stage is increasing along with an increase of processing speed (throughput). For example, in a step & scan exposure apparatus, the maximum acceleration of a wafer stage reaches 1 G.
In addition, the mass of a stage increases along with an increase in diameter of the substrate wafer. For this reason, a driving force defined by <mass of moving member (substrate wafer and stage)>×<acceleration> becomes very large, and its reaction force becomes enormous. Hence, the reaction force increases along with the increase in acceleration and mass of the moving member, and vibrations of an installation floor due to the reaction force have become non-negligible.
In order to directly solve the above problems of the reaction force, some proposals have been made.
For example, a device described in Japanese Patent Laid-Open No. 2000-206279 includes a mass body driving mechanism which reduces the reaction force generated during the stage movement. The control system of this mass body driving mechanism includes a reaction force compensation control system and position compensation control system.
Furthermore, Japanese Patent Laid-Open No. 2002-008971 describes a device that includes a stage device, which is driven by an electromagnetic actuator (linear motor) including a moving element and stator, a recoilless stage, which absorbs the reaction force by using the stator as a reaction force counter, which receives the reaction force of the moving element. The control system of this arrangement need not include the reaction force compensation control system, and only includes the position compensation control system.
In these two conventional devices described above, the reaction force generated in the horizontal direction (on an X-Y plane in the direction of the stage movement) and an offset load (inclined for the X-Y plane) about a horizontal axis can be perfectly canceled. However, the driving stroke of a mass body is a problem to cancel the rotational reaction force about the vertical axis (about a normal line of the X-Y plane).
For example, when the stage is accelerated at the position shifted from the barycenter of the stage base, in order to cancel moments generated by the stage base, mass bodies symmetrically positioned on opposing sides about the barycenter of the stage base are acceleratedly driven in the same direction as the moving direction of the barycenter of the stage.
When the stage continues to rotate around the barycenter of the stage base, the position of the mass body is shifted. Hence, a stroke for driving the mass body is required. Additionally, even if the stroke of the mass body is made long, the position of the mass body accordingly reaches the terminal end of the stroke when the moments generated by the stage base act in a single direction.
When the stage obliquely moves, the electromagnetic actuator operates while a thrust is so distributed as to avoid generating a rotational moment on each beam (guide bar). Since the thrust of the mass body in acceleration is different from that in deceleration, the mass body does not stop, and continues to move at a constant speed.
In order to avoid this situation, the position compensation control system of the mass body, in which a rotational operation amount in driving the mass body is limited, and a filter processing function is added, is proposed for the purpose of reducing the reaction force, and the like, generated during the stage movement, and reducing the driving stroke of the mass body.
Usually, in a general exposure apparatus, the moving element of the electromagnetic actuator is used as a permanent magnet, and a coil is provided in the stator in order to avoid heat conduction to the stage. Therefore, the stator serving as the reaction force counter needs to move together with a wiring of coils and cooling pipes, i.e., implementation. The implementation resistance becomes a disturbance in the stator position compensation control system serving as the reaction force counter. In the above arrangement, in which the rotational operation amount of the mass body is limited, and the filter function is added, when the implementation resistance is larger than the parameter of the operation amount, or varies at the component higher than the filter cut-off frequency, the position of the reaction force counter may shift by the disturbance.
When this position of the reaction force counter shifts, the offset load about the horizontal axis generated on the stage base by the gravity cannot be canceled, and the offset load is generated on the floor. This causes the deformation of the structure, thereby degrading the accuracy.